Sewing machine controlling apparatus

ABSTRACT

A sewing machine controlling apparatus which starts and stops a sewing machine or controls its speed in accordance with the position of an adjusting means, e.g. control pedal, for setting a sewing machine speed, as speed. The sewing machine controlled by the controlling apparatus is independent of the influences caused by changes in the pedal position signal P A  through the vibrations of the machine or through the variations in a power-supply voltage. A smooth speed switching operation, which is free from speed variations, can be realized even at a stepped switching point of the machine speed control pedal.

BACKGROUND OF THE INVENTION

The present invention relates to a sewing machine controlling apparatus, which starts, and stops a sewing machine or controls its variable speed in accordance with the position of an adjusting means for setting a sewing machine speed.

Conventionally, a system was mainly adopted of converting the position of the adjusting means of a sewing machine controlling apparatus into analog signals so as to make the analog signals into speed setting signals, and composing the speed controlling portion of analog operation around an OP amplitude circuit.

However, in recent years the development in digital IC's, etc., with microcomputers as central components is conspicuous. The speed controls have been gradually digitized for improvements in terms of cost or reliability. Thus, the detection signals of the adjusting means are naturally required to be digitized. When the pedal of the sewing machine is used as the adjusting means, various systems are used to detect and generate digital signals corresponding to the movement thereof.

However, some digital systems, which are common among the various systems and, have a fatal disadvantage in that a boundary exists where the signal changes without fail; the changes are caused between two adjacent signal values due to the variations of the sewing machine, when the pedal has been positioned on the condition of the boundary, so as to considerably vary the speed of the sewing machine, and thus making it impossible to be put into practical use.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide an improved sewing-machine controlling apparatus in which the speed setting can be smoothly switched in accordance with the position of the adjusting means, thus ensuring the stable speed operation, which is independent of the sewing-machine vibrations.

According to the present invention, a sewing machine controlling apparatus is provided so as to comprise an adjusting means for setting machine speed, a set position detecting means for converting the position of the adjusting means into a digital set position signal P_(D), a speed converting means for converting said set position signal into a speed setting signal S, a motor, whose speed is controlled in a step by step fashion in accordance with said speed setting signal S, a machine which is driven by the motor, a controlling means for controlling the machine, a timer which performs a presetting operation, wherein the shifting conditions from a speed setting signal S₁ in accordance with an optional set position signal P_(D1) to a speed setting signal S₂ in accordance with an optional set position signal P_(D2) are restricted only to a case where said set position signal P_(D2) has been maintained during a time T preset into said timer.

The object and other objects, features, aspects and advantages of the present invention become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a sewing machine controlling apparatus according to the present invention.

FIG. 2 is a chart for illustrating the principle of speed control for the sewing machine.

FIG. 3 is a time chart showing the low-speed operating condition.

FIG. 4 is a chart for illustrating the sewing machine speed with respect to the pedal position.

FIG. 5 is a flow chart showing the speed setting of the present invention.

FIG. 6 is a chart for illustrating the sewing machine speed with respect to the pedal position in the other embodiment of the present invention.

FIG. 7 is a flow chart showing the same-speed setting.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a pedal-position detecting circuit 1 is connected to a microcomputer 3 through an A/D converter 2.

The circuit 1 converts the stepping amount from the reference position of a treadle pedal 1a provided in association with a sewing machine 8 into electric signals. For example, the reciprocating operation of the pedal is converted into a revolving action. A magnet is disposed at the central portion of the pedal for operative cooperation, and a means is used for detecting the rotary angle of the magnet by employing a magnetic reluctance element. Thus, an output signal P_(A) is outputted from the circuit 1 as an analog signal. The A/D converter 2 converts the analog signal P_(A) of the circuit 1 into a digital signal P_(D) of 4 bits which is input into the microcomputer 3. The microcomputer 3 is connected to the sewing machine 8 through a pair of drivers 4 and 5 and coils 6 and 7 which constitute a means for controlling the sewing machine 8 in a central portion of the machine control. The drivers receive the outputs from the microcomputer 3 so as to drive the clutch coil 6 and the brake coil 7. A motor M is provided in association with the sewing machine 8 as a so-called electromagnetic coupling construction wherein the motor transmits the turning effort of a motor main-body, which is always rotating at a high speed, to an output shaft through the magnetic circuit due to the excitation of the clutch coil 6; the motor changes the sliding speed with respect to the rotary portion of the motor main-body by the intensity of the exciting current so as to thereby perform the speed controlling operation, and the motor stops the output shaft through the magnetic circuit due to the excitation of the brake coil 7. The sewing machine 8 is normally coupled to the output shaft of the motor through a pulley and a belt. A needle position detecting circuit 9 is provided between the microcomputer 3 and the sewing machine 8, and is adapted to adjust a magnet piece, engaged with the shaft end of the sewing machine 8, in accordance with the needle-above position to rotate it in synchronous relationship with respect to the rotation of the machine shaft. The needle-above position is detected, by a hall effect IC which is provided in association with the circuit 9 and which is disposed in a stationary position opposite to the magnet piece so as to output a needle-above signal NU. A frequency generator 10 is connected between the microcomputer 3 and the sewing machine 8 together with a wave-form shaping circuit 11 and is normally engaged with the machine shaft end so as to output signals which have a period which is to be varied in accordance with the rotational speed of the sewing machine. The wave-form shaping circuit 11 is composed of a circuit having a comparator used for shaping the signals which are to be outputted from the frequency generator into rectangular-wave pulse signals FG. The pulse signals FG of the circuit 11 are inputted into the terminal iNT of the microcomputer 3.

The operation of the above-described apparatus will be described hereinafter.

Once the pedal is stepped on by the operator so as to move it from its reference position, the amount of motion is detected by the pedal-position detecting circuit 1 so as to thereby output an analog signal P_(A). The analog signal P_(A) is converted into a set position signal P_(D), which is a digital value of 4 bits, by the A/D converter 2.

The microcomputer 3 converts the set position signal P_(D), if the value of the set position signal P_(D) is a normal value or more, into numerical value, i.e., speed setting signals S, causing the frequency-division of the pulse signal FG by a ROM table to be described later; a frequency-division value is stored in a RAM (RAM1); a signal CL excites a clutch coil 6 through the driver 4 so as to thereby drive the sewing machine 8.

After operating the sewing machine 8 as described hereinabove, the pulse signals FG are outputted into the input terminal iNT of the microcomputer 3 through the frequency generator 10 and the wave-form shaping circuit 11. The microcomputer 3 divides the input in frequency by the number stored in the above-described RAM1, and measures the frequency-divided period, and effects an assignment operation in an operation formula to be described later so as to control the exciting time of the clutch brake of the section of the following pulse signal FG. The speed controlling operation for the sewing machine 8 is performed while the measurement and controlling operations within the microcomputer 3 are being repeated. Accordingly, the sewing machine 8 is operated at a speed in accordance with the analog signal P_(A) outputted through the detection by the pedal-position detecting circuit 1.

Then, when the pedal is returned towards the reference position and the set position signal P_(D) becomes smaller than the normal value, a low speed is set and the brake coil 7 is excited through the driver 5 so that the sewing machine 8 is rapidly reduced in speed to the low speed. When the sewing machine 8 becomes slower in speed, the clutch coil 6 is turned off at a time point when the needle-above signal Nu from the needle-position detecting circuit 9 has been outputted so as to excite the brake coil 7 for a given time so that the machine 8 comes to a stop in the needle-above position.

Thus, the series of operations of finishing a needlework, replacing it by the new needlework, and starting to sew it are adapted to be effected. The first embodiment of the present invention will be described in detail hereinafter with reference to the drawings of FIG. 2 and the subsequent description.

FIG. 2 and FIG. 3, which are charts showing the principles of controlling the speed, will be described hereinafter with reference to the drawings.

The operation formula of T_(CB) =AT_(P) -B as shown in FIG. 2 uses a straight-line system for simplification of the operation, in which the A is a constant corresponding to the gain of a normal system and the B is a constant which can make fine adjustments of the speed; the values of A and B are determined by taking the safety and response of the system into consideration.

Referring to FIG. 2, the measured period T_(P) after the frequency division of the pulse signal FG is first measured and is substituted into the operation formula. The clutch coil, if the operation results are positive, or the brake coil, if they are negative, is excited for a period after the frequency division of the following pulse signal FG only for the time of the operation results. Namely, when the measured period T_(P) has been varied in a smaller direction, i.e., when the sewing machine has been varied onto a high-speed side, the on time duty cycle of the clutch is reduced. As the case may be (if a value of T_(P2) or lower occurs), the brake is thrown and operates to prevent the speed from being made higher. When the measured period T_(P) has been varied in a larger direction, i.e., when the sewing machine has been varied onto a low-speed side, the on time duty cycle of the clutch is increased. The controlling operation is performed so as to prevent the speed from becoming lower. A safety operation is effected at a point d (measured period T_(P1), clutch-on time T_(C1)) just matched to the machine load in this manner.

The above-described condition is shown in FIG. 3. Referring to FIG. 3, the stable operating condition at a low speed N_(P) is shown. A safe operation is effected at such a duty cycle as the clutch coil exciting signal CL may be outputted by T_(C1) to the period T_(P1) of the pulse signal FG.

When the pulse signal FG has been divided in frequency within the microcomputer 3 as described hereinabove, the measured period T_(P) rapidly increases and accordingly, the engagement ratio of the clutch increases to accelerate the sewing machine. Assuming that the machine load torque in the increased speed remains almost unchanged, then the last clutch on time duty cycle becomes the same as during the operation at the low speed N_(P). The operation is effected at an approximation of the point d. Namely, assuming that the time of the frequency dividing operation is 1, then the operation is effected at a speed which is twice as fast as the low speed N_(P).

The construction example of the ROM table for conversion to the speed setting signal S (frequency-division time value) from the set position signal P_(D) is shown below.

                  TABLE I                                                          ______________________________________                                         Set Position                                                                              Speed Setting Signal S                                              Signal P.sub.D                                                                            (frequency-division number value)                                   ______________________________________                                         0          *(0)                                                                2                                                                              3          0                                                                   4                                                                              5                                                                              6          1                                                                   7                                                                              8          2                                                                   9          3                                                                   10         4                                                                   11         6                                                                   12         8                                                                   13         10                                                                  14         13                                                                  15                                                                             ______________________________________                                    

The speed setting signal (0) of the * mark in the table I shown above is required only during the shifting time from the driving operation to the stop condition. The 0, 1, 2 of the setting position signals P_(D) corresponding to the * mark are distinguished as the stop instruction regions by a special program.

The relationship of the set position signal P_(D) with respect to the machine speed in accordance with the speed setting signal S converted as shown in the table shown above is shown as a graph in FIG. 4.

The machine speed N_(M) shown here is represented in the following formula in accordance with the above-described principle.

    N.sub.M =N.sub.P ×(S+1)                              (1)

Referring to FIG. 4, in the above-described control, the one stage portion of the reference speed N_(P) suddenly changes at the machine speed, particularly in the 3 or higher region, i.e., the driving instruction region, of the set position signal P_(D), for example, in the boundary between 5 and 6, or 7 and 8. If the pedal is positioned to become the boundary, large speed variations of the reference speed N_(P) are caused by the vibration of the machine or the slight change in the power-supply voltage. The embodiment wherein measures are taken against the speed variation by the use of a timer, which is one of the characteristics of the present invention will be shown in the flow chart of FIG. 5.

Referring to FIG. 5, the set position signal P_(D1) is newly read at the 12, the check is made as to whether it stays within the stop instruction range of 0 through 2 at 13, and it goes to a stop processing routine when it stays within the stop instruction range. If it does not stay within the stop instruction range, the driving condition of the machine continues. Then, at 14, it is compared with a previously read set position signal P_(D2). If it is not an adjacent value or when time passes by "T" if it is an adjacent value, the timer stops at the 15 and set newly read position signal P_(D1) is adopted. If this is not the case, a time "T" is preset in the timer at 17 to start the timer so as to thereby adopt the set position signal P_(D2). After the above-described timer has been started, it is preset by a special timer-interrupt processing routine (not shown). When it has been started, it is always clocking.

At 18, it is converted from the set position signal P_(D1) or P_(D2) adopted as described hereinabove into the speed setting signal S by the ROM table and moves to the following processing.

The processing shown in the flow chart is inserted into one portion of the control processing loop during the machine driving operation. Accordingly, when the newly read set position signal P_(D1) is a value adjacent to the conventional set position signal P_(D2), the condition is not rendered effective until the condition continues for at least a time T.

In the setting of the time T, the reply to the motion to the respective adjacent pedal positions is delayed when too long a time is set. It is considered easy to set a time T which is not subject to the influences caused by vibration in the normal machine operation or by changes in the instantaneous analog signal P_(A) through the power-supply variations, and which is independent of the reply delay. Also, in the normal sewing operation, it is ordinary that the operation wherein the value of the set position signal P_(D) considerably changes is effected, especially in the sewing operation demanding the response property. The time T is neglected in such a case as described hereinabove and the ready answer can be given. It is considered that the time T can be set to a sufficiently long time.

The above-description is given about a case where the pedal is used as an adjusting means for setting the machine speed. The present invention is effective even where a variable volume for restricting the highest speed of the machine is used as the adjusting means, and the set position signal is provided through the A/D conversion, or where the set position signal is adapted to be made directly by a code switch.

Then, the second embodiment of the present invention will be described hereinafter with reference to FIG. 6 and FIG. 7. The ROM table for conversion to the speed setting S (frequency-division number value) from the set position signal P_(D) is in two types as shown in Table II and Table III. The relationship of the machine speed with respect to the set position signal P_(D) will be described as graph in FIG. 6. Referring to FIG. 6, the solid line is shown in accordance with the ROM table 1, while the broken line is shown in accordance with the ROM table 2.

                  TABLE II                                                         ______________________________________                                         (ROM Table 1)                                                                               Speed Setting                                                                  Signal S                                                                       (Frequency-                                                       Set Position Division Number                                                   Signal P.sub.D                                                                              Value)                                                            ______________________________________                                         0            *(0)                                                              2                                                                              3                                                                              4                                                                              5                                                                              6            0                                                                 7                                                                              8                                                                              9                                                                              10                                                                             **11                                                                           12           1                                                                 13                                                                             14                                                                             **15                                                                           16           2                                                                 **17                                                                           18           3                                                                 **19                                                                           20           4                                                                 **21                                                                           22           6                                                                 **23                                                                           24           8                                                                 **25                                                                           26           10                                                                **27                                                                           28           13                                                                29                                                                             30                                                                             31                                                                             ______________________________________                                    

                  TABLE III                                                        ______________________________________                                         (ROM Table 2)                                                                               Speed Setting                                                                  Signal S                                                                       (Frequency-                                                       Set Position Division Number                                                   Signal P.sub.D                                                                              Value)                                                            ______________________________________                                         0            *(0)                                                              2                                                                              3                                                                              4                                                                              5                                                                              6            0                                                                 7                                                                              8                                                                              9                                                                              10                                                                             **11         1                                                                 12                                                                             13                                                                             14                                                                             **15         2                                                                 16                                                                             **17         3                                                                 18                                                                             **19         4                                                                 20                                                                             **21         6                                                                 22                                                                             **23         8                                                                 24                                                                             **25         10                                                                26                                                                             **27         13                                                                28                                                                             29                                                                             30                                                                             31                                                                             ______________________________________                                    

Two types of ROM tables 1 and 2 are different only in the portion marked with **, i.e., the portion where the speed setting signal S is switched. The speed setting speed signal (0) of the * mark in the same table is necessary only at the motion from the driving condition to the stop condition. The 0 through 5 region of the set position signal P_(D) corresponding to the * mark is distinguished as a stop instruction region in accordance with a special program.

The selecting means of two ROM tables are shown in the flow chart of FIG. 7. The operation will be described hereinafter in accordance with the same drawing.

At first, at 19, the set position signal P_(D1) is newly read, and a check is made as to whether the P_(D1) stays within the stop instruction range at 20, it goes to a stop processing routine if it stays within the range; the driving condition of the machine will continue if it does not stay within the stop instruction range. Then, at 21, the check is made as to whether or not the newly read set position signal P_(D1) is equal to a value shown with a ** mark in Table II and Table III. If so, a check is made as to whether or not the value is smaller by 1 than the P_(D2) previously read at 22. If so, it is converted to the speed setting signal S by the ROM Table 2 at the 23. Also, when it was any value except for a value shown with the mark ** at 21, the conventionally stored data of P_(D2) is newly set in the P_(D1) at the 24. It is converted into the speed setting signal S by the ROM table 1 at 25, and the program moves to the following processing.

The processing shown in the flow chart of FIG. 7 is inserted into one portion of the control processing loop during the machine driving operation. To make the operation short, the ROM Table 2 is adopted only when the newly read set position signal P_(D1) is smaller by 1 than the conventional set position signal P_(D2) and is in the switching portion (the value of the ** mark of Table 1 or Table 2) of the speed signal, to provide the broken line of the machine speed of FIG. 6. With the exception of the above description, the ROM table 1 is adapted to provide the solid line machine speed of FIG. 6.

Under such a construction as described hereinabove, the set position signal portion, shown with the ** mark, or the switching portion of the machine speed effects its hysteresis operation. Accordingly, when the range of the analog signal P_(A) corresponding to the value of the ** mark is kept sufficiently large, the machine speed can be independent of the vibrations of the machine.

The above-description is given about a case wherein the pedal is used as the adjusting means for setting the machine speed. The present invention is effective when the variable volume for restricting the maximum speed of the machine is used as the adjusting means, and the set position signal is provided through the A/D conversion, or even when the set position signal is adapted to be provided directly by a cord switch.

As apparent from the above-description, the present invention provides a sewing machine controlling apparatus, which is independent, in machine speed, of the influences which are caused by changes in the pedal position signal P_(A) through the vibrations of the machine or the variations in the power-supply voltage. The smooth speed switching operation, which is free from the speed variation, can be realized even in the stepped switching point of the machine speed, thus resulting in greater advantages.

Although the present invention has been described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modification are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of this invention unless they depart therefrom. 

What is claimed is:
 1. A sewing machine controlling apparatus, comprising an adjusting means for setting a machine speed, a set position detecting means for converting the position of said adjusting means into a set position signal P_(D) which is a digital value, a speed converting means for converting said set position signal into a speed setting signal S, a motor whose speed is controlled in a step by step fashion in accordance with said speed setting signal S, a sewing machine to be mechanically driven by said motor, a controlling means for controlling the machine, a timer, wherein said apparatus shifts from a speed setting signal S₁ which corresponds to an arbitrarily set position signal P_(D1) to speed setting signal S₂ which corresponds to another arbitrarily set position signal P_(D2) only after the lapse of a time period T, said time period T being measured by said timer.
 2. A sewing machine controlling apparatus in accordance with claim 1, wherein said time period T is set equal to zero in a case where said set position signals P_(D1) and P_(D2) differ by more than a predetermined value. 